Storage batteries of the lead-acid class customarily include positive and negative plates having grid structures which are supported in spaced relation in an electrolyte with an active material located around portions of the grid structures. As is well known by those skilled in the art, electrical energy is converted into chemical energy which is stored in the battery during charging and reconverted into electrical energy when the battery is discharged by means of the well known double sulfate reactions.
In such a battery corrosion of the positive grid structure tends to occur at vulnerable areas particularly at those points where internal stresses have been created during manufacture of the grid. These stresses tend to be maximized at "inside corners" of the lead alloy grid structure, i.e., those portions of the grid structure where surfaces intersect at some angle less than 180.degree.. In this way battery life becomes materially shortened.
In providing a battery of longer operating life particularly under deep cycling conditions, it has been proposed to utilize a positive grid structure having an antimony grid content. However, while antimony improves the functions of the active material at the positive plate, particularly under a deep discharge, as well as strengthening the grid structure, a problem may arise. During charging the surfaces of the positive grid structure will release antimony. Some of this antimony is released from those positive grid surfaces in contact with active material in which it will be released. The remaining antimony released, i.e., that released without inhibition from grid surfaces not covered by active material, will be electrochemically attracted to the negative plate and deposited thereon producing contamination of the negative active material. When this contamination of the negative active material takes place, battery life is again significantly shortened. Also during discharge, antimony will be released from the surfaces of the negative grid structure into the electrolyte, and during recharge, will be electrochemically redeposited on the surfaces of the negative plate including its active material (which has a substantially greater area) thus causing similar contamination and subsequent shortening of battery life.
This shortening of battery life occurs because the electrical potential required to disassociate the hydrogen and oxygen components of the electrolyte due to electrolysis is materially lowered by such contamination. This in turn necessitates more frequent addition of water to the electrolyte and, when the battery is to be charged to a constant potential or "back EMF", a greater portion of the charging current is used up by gassing (electrolysis) and overcharging of the battery plates. Since overcharge is the primary cause of battery failure and, since gassing will increase the specific gravity of the electrolyte thereby accelerating corrosion of the positive grid parts, it will readily be seen that material reduction of antimony contamination of the negative active material will substantially increase battery life.
In addition, when the surfaces of a grid having an antimony content are exposed to the electrolyte during electrochemical formation and subsequent charging, a poisonous gaseous compound known as stibine (SbO.sub.3) may be released from the cell into the atmosphere. This may become an occupational hazard in some cases and furthermore, if a battery with grids having an antimony content is provided with a catalytic recombination device of conventional nature, poisoning of the catalytic device may result thus causing failure of the recombination process.
Also in conventional practice, when electrochemically forming positive and negative plates in an acid bath and the positive plate grid structure has an antimony content, it is necessary to employ separate formation containers for the positive and negative plates.
Furthermore, when electrochemically forming a positive plate in an acid bath as noted, its post or burning lug becomes coated with a film of PbO.sub.2. This coating or film must be removed with added expense and trouble in order to provide a clean lead surface for burning or for attaching a terminal clamp.
Finally, if a battery having a low maintenance characteristic is constructed having grid structures formed with little if any antimony content, these grid structures are relatively soft which presents difficulties in plate manufacture and which invites strengthening in some manner.
Various attempts have been made in the art to solve the corrosion problems indicated. However, an extensive study of prior art disclosures has failed to uncover a lead-acid battery construction wherein there is found a grid structure and grid complement means in the form of an enclosure body which overlies and protectively reinforces all portions of a grid structure not in contact with active material.
It is well known in the art to utilize a protective means at certain points in a battery of the lead-acid class.
For example, U.S. Pat. No. 1,128,232 discloses a top bar and lug protector for a flat plate design which snaps into position, but as noted in line 57, page 2, the lug protection extends only to the strap.
U.S. Pat. No. 1,171,597 shows a top protector that slips over plate and separators to hold the parts together. However, the patent stresses openings 4 to permit electrolyte circulation rather than preventing it.
U.S. Pat. No. 1,051,147 shows protector means for frame and top bar parts of a flat or pasted plate but does not protect post means.
U.S. Pat. No. 1,379,854 discloses a celluloid sleeve shrunk over post means only and cemented to the cell cover.
U.S. Pat. No. 1,580,596 discloses a post projector molded on the underside of the cell cover and enjoins the strap member but no protection for grid surfaces.
U.S. Pat. No. 2,120,822 discloses protective sleeves for the post means of a mine lamp battery and has no grid protection.
U.S. Pat. No. 1,940,976 discloses perforated protector means for a grid and no protection for the lug.
Other patents disclosing partially protected grid structures include U.S. Pat. Nos. 2,420,456, 2,647,157, 2,570,677, 1,605,968, 1,586,406, 1,422,815, 3,944,432, 1,364,011, 1,158,491, 3,247,023, 2,490,630 and 3,813,300.
None of these patents appear to disclose the concept of combining a grid structure with grid complement means arranged to protectively enclose all surfaces of the grid structure which are not in contact with active material so as to retard corrosion and in some cases prevent release of antimony at some of the grid surfaces.